3 about 18 minDeep Learning viewOpenStax 7.3Netter p.187–190BodyParts3D

Discs, facet joints and ligaments: how the pieces are held together

Two neighbouring vertebrae meet at three joints: one disc between the bodies and a pair of small synovial joints between the arches. Ligaments run the length of the column over both.

The intervertebral disc

An intervertebral disc is a pad of fibrocartilage that joins the bodies of two neighbouring vertebrae. The joint is a symphysis, a secondary cartilaginous joint. Each disc has two parts. The anulus fibrosus is a tough fibrous ring that anchors one body to the next. Inside it is the nucleus pulposus, a softer gel with a high water content, which resists compression and changes shape as one vertebra tilts on the other.

Discs are found from the axis to the sacrum. The highest is C2–C3 and the lowest is L5–S1; there is none above or below the atlas, and none between the fused sacral segments. That makes 23, and all 23 are separate pieces on the specimen. Select a few in the Column alone view and compare them: the discs are thin in the neck and thickest in the lumbar region, where the load is greatest.

Facet joints and the intervertebral foramen

Behind the disc, the arches of two neighbouring vertebrae meet at a pair of zygapophysial (facet) joints. Each is a small plane synovial joint between the inferior articular process of the vertebra above and the superior articular process of the vertebra below, wrapped in a thin capsule. The surfaces glide on each other, and their direction in each region guides the movement that region allows.

Between the disc in front and the facet joint behind lies the intervertebral foramen. Its roof and floor are the notched pedicles of the two vertebrae. A spinal nerve leaves the vertebral canal through it, which is why trouble in either neighbour, a bulging disc in front or an arthritic facet joint behind, can press on the nerve.

One level, three joints

  1. Disc between the two bodies (symphysis): bears weight
  2. Left and right facet joints between the arches (plane synovial): guide movement
  3. Intervertebral foramen between them at each side: the spinal nerve's exit
Netter p.187–188, 225–226

The long ligaments (taught in words)

The ligaments of the column are not part of this model, so this subtopic has no specimen to point at. Learn them by where they lie relative to the parts you can see.

Ligaments of the vertebral column, from front to backNetter p.189–190OpenStax 7.3

  • Anterior longitudinal

    Where it runs
    Down the front of the bodies and discs, the whole length of the column
    What it limits
    Extension. The stronger of the two longitudinal ligaments

  • Posterior longitudinal

    Where it runs
    Down the back of the bodies and discs, inside the vertebral canal, in front of the spinal cord
    What it limits
    Flexion

  • Ligamentum flavum

    Where it runs
    Between the laminae of neighbouring vertebrae, behind the spinal cord; elastic
    What it limits
    Flexion; helps restore the upright posture

  • Interspinous

    Where it runs
    Between neighbouring spinous processes
    What it limits
    Weak

  • Supraspinous

    Where it runs
    Along the tips of the spinous processes; in the neck it broadens into the nuchal ligament
    What it limits
    Flexion

When a disc herniates

If the back of the anulus fibrosus weakens, with age or injury, pressure on the disc can push the nucleus pulposus backward through it. This is a herniated (“slipped”) disc. The bulge lies beside the intervertebral foramen and can compress a spinal nerve, giving pain, and sometimes weakness or numbness, in the part of the body that nerve supplies.

Where discs herniate most oftenNetter p.181–182, 185–186OpenStax 7.3

  • Lumbar (the most common)

    Usual levels
    L4–L5 and L5–S1
    Typical result
    Pain down the back of the thigh and leg (sciatica). L4–L5 may compress the L5 root; L5–S1 may compress the S1 root

  • Cervical

    Usual levels
    C5–C6 and C6–C7
    Typical result
    Pain in the neck, shoulder and upper limb

Worked case · A box lifted badly

A 41-year-old man bends forward to lift a heavy box and feels a sudden pain in his lower back. Over the next day the pain spreads down the back of one leg to the foot.

Which two discs would you look at first, and why does pain appear in the leg when the injury is in the back?

OpenStax 7.3Netter p.185–186

Knowledge check · 3

Answer, read why, and try again whenever you like. Answers are kept in both study modes.

0 of 7 correct
  1. Q1Parts of a discOpenStax 7.3Netter p.187–188

    Which part of an intervertebral disc is the gel-like centre that resists compression?

  2. Q2Extent of the discsNetter p.179–180, 187–188

    Between which two vertebrae is there no intervertebral disc?

  3. Q3Facet jointsNetter p.187–188, 225–226

    What kind of joint is a zygapophysial (facet) joint?

  4. Q4Longitudinal ligamentsNetter p.189–190OpenStax 7.3

    Which ligament runs down the front of the vertebral bodies and limits extension of the column?

  5. Q5Lumbar disc herniationNetter p.185–186

    MRI of a patient with pain down the back of the leg shows a herniation of the disc between the fifth lumbar vertebra and the sacrum.

    Which nerve root is this herniation most likely to compress?

  6. Q6Nuchal ligamentOpenStax 7.3

    In the neck, the supraspinous ligament broadens into which structure?

  7. Q7Naming a discBodyParts3D
    The column alone from the patient's left. One vertebra in the lower part of the column is highlighted.

    Column alone, left lateral view. Ribs, cartilages and sternum hidden. The patient's left side: the front of the body is toward your left.

    The picture shows the column alone from the patient's left, with one vertebra highlighted. Which disc lies directly below it?

Previous2 Regional vertebraeNext4 Thoracic cage